Rotary contactor with a short strip, in particular for motor vehicles

ABSTRACT

The invention concerns a rotary contactor comprising a fixed casing which houses a movable hub and a flexible strip attached at one end to the hub and at its other end to the casing. An internal rotor is disposed radially between the hub and the internal bore of the casing. A planetary gear train supported by the casing, the internal rotor and the hub is provided for rotating the internal rotor via the hub. The internal rotor comprises means for the passage of the flexible strip. The invention is useful for motor vehicles.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION

The present invention relates to rotary contactors, especially for motorvehicles, of the kind comprising two coaxial parts which are mounted forrotation of one with respect to the other against the action of anelectrically connecting flexible tape which is wound in a spiral betweenthe said parts, being attached at one of its ends to one of the saidparts and at its other end to the other one of the said parts.

Such a contactor is described for example in the document EP-A-0 479567.

BRIEF SUMMARY OF THE INVENTION

Thus, in FIG. 11, there is shown at 100 an exploded view of a rotarycontactor comprising a fixed part 101, 102 in the form of a housingfixed to the steering column of the motor vehicle, via the switchsupport which is located under the steering wheel and which is fixed tothe end of the steering column.

This contactor includes a movable part 103 in the form of a hub, whichis mounted for rotation on the base plate 102 of the housing 101, 102.The hub includes a chimney 106 which is adapted to be driven in rotationby the steering wheel of the vehicle, and which also constitutes aconnector.

In practice, the hub 103 is mounted within the hollow housing whichcomprises the components 101, 102.

One end of the flexible tape 104 is attached to the said chimney 106,while the other end of the flexible tape 104 is attached to the baseplate 102 of the fixed part.

In the known way, the flexible tape 104 comprises one or more electricalconductors 105, together with an insulator for insulating the conductors105 from each other.

This tape 104 provides electrical connection between the two parts 101,102-103 without any micro-fractures.

The rotary contactor 100 ensures electrical connections for the purposeof, for example, controlling an inflatable airbag for protecting

the driver, or for controlling the horn from the steering wheel. All ofthis depends on the application.

With this type of contactor, a problem arises because it is necessary tobe able to execute for example 2.5 turns of the steering wheel in onedirection and 2.5 turns of the steering wheel in the other direction.

Thus, the tape is spiral wound on the hub and is unwound on the housingin the same way as a watch spring. It has to be of substantial length,in order to satisfy the need for rotation of the order of five (5) turnswhich is necessary in most motor vehicles, this rotation being limitedby abutments or by the tension in the tape.

The length of the tape is thus variable according to the diameters forinternal winding and external unwinding which are determined by the sizeof the contactor.

In general terms, the length of these tapes is of the order of 3 to 6meters, and represents a major part of the cost of the rotary contactor,especially in terms of the number of electrical paths or conductors 105that are provided by the said tape 104. More than half of the price canbe due to the tape in some cases.

It is also desirable to reduce the radial overall size of such acontactor fitted below the steering wheel in a position close tonumerous electrical devices such as switches.

In practice, the internal diameter of the hub 103 is a function of thediameter of the steering shaft which passes through the fixed steeringcolumn of the vehicle.

Thus the internal diameter of the rotary contactor has a value which isimposed by external considerations.

In order to demultiply the number of turns between the hub and thehousing, and to reduce the length of the tape, it has previously beenproposed, in the documents U.S. Pat. No. 5,171,573 and EP-A-O 478 455,to provide the rotary contactor with an epicyclic gear train, with atleast one pinion which is arranged to mesh with a set of internal teethof the housing and with a set of external teeth of the hub.

In practice these pinions are of extended length, so as to carry rollersor bearings for guiding the flexible tape. For example, in the documentEP-A-O 478 455, the flexible tape forms a U-shaped loop which is engagedon the bearings.

The tape is thus in discontinuous contact with the rollers or bearings,so that it is subjected to stresses which are detrimental to the usefullife of the contactor.

In addition, the nature of this arrangement is such as to increase theheight of the contactor, and this complicates the manufacture of thepinion.

An object of the present invention is to provide, in a simple andinexpensive way, a rotary contactor having reduced radial size andheight, with a short tape which winds under good conditions, while alsosimplifying the pinion of the epicyclic gear train.

According to the invention, a contactor of the type described above ischaracterised in that the pinion is carried in rotation by an innerrotor of hollow annular form having an axially oriented annular skirt,in that the inner rotor is mounted in rotation on the movable hub, beingmounted within the fixed housing, in that there is a space between themovable hub and the internal bore of the skirt of the inner rotor, foraccommodating the tape and for winding of the latter around the movablehub, and in that the skirt of the inner rotor has passage means for theflexible tape, the latter being adapted to wind on to the skirt.

Thanks to the invention, the total size of the rotary contactor can bereduced in a simple and inexpensive way by taking as a basis theinternal diameter of the hub, which is defined by the manufacturer'scost requirements, and the number of turns which the steering wheel hasto make, while providing electrical continuity without anymicrofractures, by virtue of the short electrical connecting tapewinding under good conditions on the hub and the inner rotor.

In this connection, thanks to the invention, and more particularly tothe epicyclic gear train, it is possible as a consequence to reduce thelength of the tape which is employed, because of the demultiplicationeffect on the number of turns between the fixed part (i.e. the housing)and the movable part (i.e. the hub), thus reducing the selling price ofthe contactor and minimising the cost of the components and assemblytimes, the housing and the hub being of simple forms.

Also reduced are the noises due to the length of the tape, while fittingof the contactor is made easier. The tape winds in a circular path on tothe hub and the inner rotor. It is therefore well supported, and ispreserved, thus prolonging the useful life of the contactor. The pinionis simplified.

In accordance with another feature of the invention, the rotarycontactor further includes, within the fixed housing, an outer rotorwith a disconnectable rotary drive system between the two rotors, suchthat the epicyclic gear train is of a double differential type.

This arrangement enables the length of the flexible tape to be reducedeven more.

BRIEF SUMMARY OF THE DRAWINGS

Further features and advantages of the invention will appear in thelight of the following description, given with reference to the attacheddrawings, in which:

FIG. 1 is an exploded view of the rotary contactor without its flexibletape;

FIG. 2 is a view similar to FIG. 1 but viewed in the other axialdirection:

FIG. 3 is a diagrammatic view of the rotary contactor, showing thelatter in one of its extreme positions of engagement, with the tapeunwound;

FIG. 4 is a view similar to FIG. 3, showing the rotary contactor in thefully unwound position in the other of its extreme positions;

FIG. 5 is a view similar to FIG. 3 showing the rotary contactor in amiddle position (with the steering wheel turned to the right);

FIG. 6 is a partial view of the contactor without the hub, shown in itsposition corresponding to that of FIG. 5;

FIG. 7 is a partial view similar to FIG. 6, for the position of thecontactor which corresponds to that in FIG. 3;

FIG. 8 is a view similar to FIG. 6, for the position of the contactorcorresponding to that in FIG. 4;

FIG. 9 is a diagrammatic view showing the various positions of the drivefinger for, respectively, the extreme positions of engagement and themean position;

FIG. 10 is a perspective view of the tape;

FIG. 11 is an exploded diagrammatic view of a contactor in accordancewith the prior art.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 9 show a rotary contactor for a motor vehicle, of the kindcomprising two coaxial parts 2, 7 which are mounted for rotary movementof one with respect to the other against the action of a flexible,electrically connecting, tape 8, which is wound in a spiral between thesaid parts, being attached to one of the ends of one of the parts and tothe other end of the other one of the parts.

In this example, one of these parts comprises a rotatable hub 2 which isadapted to be coupled in rotation to the steering wheel of the vehicle,together with a fixed housing 7, which is fixed to the fixed steeringcolumn of the vehicle via the switch support which is located below thesteering wheel and which is not shown. The housing 2 is mounted withinthe hollow housing 7.

With a view to reducing the length of the flexible tape 8, and reducingthe overall external size of the housing 7, in accordance with onefeature of the invention the rotary contactor includes an inner rotor 5,of hollow annular form, which is mounted in rotation on the hub 2 andaccommodated in the housing 7, together with a train of epicyclic gears40, 20, 4 carried by the fixed housing 7, the movable hub 2 and theinner rotor 5, so as to drive the inner rotor 5 in rotation through thehub 2, and so as to reduce the number of turns between the movable hub 2and the fixed housing 7.

The inner rotor has passage means 51 for the flexible tape 8. Thesemeans 51 consist in this example of a slot to be described later herein.In another version, they may consist of a window.

More precisely, in the drawings the rotary contactor comprises anassembly of components of plastics material, namely a ring 1, themovable hub 2, a finger 3, a pinion 4, the inner rotor 5, an externalrotor 6, and the housing 7. The rotors 5, 6 are of hollow annular form,as is the housing 7, the form of which is simple.

These components are preferably made by molding. The housing 7 is aone-piece component in this example, by contrast with that in FIG. 11,and it includes a base 74, oriented transversely and joined at its outerperiphery to an axially oriented annular skirt 72. The base 74 has acentral hole at its inner periphery, and is formed with an axiallyprojecting central portion 70 in the form of a tubular sleeve.

The skirt 72 includes within it an internal set of teeth 40 formed inits internal bore, with a smooth, transversely oriented, wall 71projecting radially towards the axis of the assembly from the set ofteeth 40 and carrying an axially projecting ramp 30. The internal boreof the skirt 72 is thus stepped, with a cylindrical portion which isjoined through the wall 71 to the set of teeth 40 which are shallow butof greater internal diameter. The set of teeth 40, the teeth of whichare arranged on a pitch circle, together with the ramp 30, which is oftriangular (pointed) form with a rounded summit, are formed at the freeend of the housing 7, that is to say in the upper part of the latter.

This housing, being of simple molded form, also has a side aperture 73of substantially rectangular form, to enable the flexible electricallyconnecting tope to pass outside the housing and to provide connection tothe associated integrated circuitry. In this example, a chimney (whichis not shown, in the interests of simplicity) extends radially outwardlyfrom the aperture 73.

The fixed housing 7 is thus of annular hollow form, and in this example,in the interests of simplicity, the ears whereby the housing 7 isfastened to the switch support, located under the steering wheel of thevehicle and connected to the end of the steering column, are not shown.In another version, the housing 7 may be formed directly in the centralpart of the said switch support, which reduces the number of componentsrequired.

The annular hollow rotors 5, 6 are mounted within the housing 7, and theelectrically conductive flexible tape 8 is wound on and off theserotors, the tape including, encapsulated within an electrical insulator,a number of electrical paths or conductors, such as flattened conductivewires, the number of which is predetermined as a function of theapplication and the number of items of information to be transmittedbetween the fixed steering column and the rotatable steering wheel. Thetape partly determines the thickness of the rotary contactor.

The ends of the conductive tape 8 are fixed, respectively, to a portion80 of the housing 7 and a portion 81 of the movable hub 2, which isrotated by the steering wheel of the vehicle. The hub 2 is mounted forrotation on the housing 7 by means of the central chimney 70 of thelatter. More precisely, the hub 2 is engaged through its inner peripheryon the outer periphery of the chimney 70. The hub 2 has at one of itsends, namely its upper end, a transversely oriented flange 21 which isarranged to close off the housing 7.

It will be noted that the driving chimney (projecting radially) of thehub 2, for coupling the hub 2 in rotation with the steering wheel of thevehicle, has not been shown here. For more detail, reference should bemade to FIG. 11. In this example the chimneys of the housing 7 and hub 2are adjacent to the portions 80. 81.

The inner rotor 5 is centered by, and pivots around, the hub 2. Therotor 5 is generally in the form of a ring and includes an axiallyoriented annular peripheral skirt 52, which is joined at one of its ends(namely its upper end--FIG. 1) to a transverse flange 54. This flange 54carries an integral pivot 53 which projects axially in its upper part onthe side opposed to its skirt 52, the pivot 53 being in this example inthe form of a spigot arranged to receive the pinion 4, together with abridge element 31 whereby a finger 3, which is acted on by a returnspring 36 (FIG. 8), is retained and articulated.

For this purpose, the bridge element 31 includes (see FIGS. 6 to 8)cradle portions for receiving trunnions 32 formed on the finger 3 atthat one of its axial ends that is the closer to the hub 2. The otherend of the finger 3 is wedge-shaped. The finger has a spigot which is infacing relationship with another spigot carried by the bridge element 31for mounting and centering, between the two heads, the return spring 36,which in this example is in the form of a coil spring. Thus the coilspring bears on the bridge portion of the bridge element 31 at one ofits ends, and on the finger 3 at its other end, so as to maintain thesaid finger 3 constantly in a lower position, that is to say in contactwith the base of a slot which is formed in the skirt 52 and whichinterrupts the flange 54 in the region of the bridge element 31.

In practice, the flange 54 constitutes a thickened portion which definesan annular rib at the outer periphery of a transversely oriented baseportion 55 (FIG. 1) which is part of the rotor 5 in its upper region andwhich has a central hole. At its inner periphery, this base portion 55has an integral portion constituting an axially thickened portion in theform of a centering sleeve 56. The bridge element 31 includes two kneeportions which join the flange 54 to the sleeve 56, the internaldiameter of which is smaller than that of the skirt 52. It is in theseknee portions that the cradle elements for receiving the trunnions 32are defined.

In the region of the flange 54, the bridge element 31 projects in axialsuperelevation, and has a generally U-shaped cross section, with twoaxially oriented branches anchored in the flange, together with a baseportion which joins the two branches together and constitutes the abovementioned bridge portion on which the spring 36 bears. The branches ofthe U provide good retention for the finger 3.

It will be noted that it is the sleeve 56 that enables the inner rotor 5to be mounted rotatably on the hub 2, so that, in accordance with onefeature of the invention, there is a space between the hub and theinternal bore of the skirt 52, to accommodate the tape and to enable thelatter to be wound around the hub 2. The tape is thus protected by therotor 5.

It will be noted that the wedge-shaped end of the finger 3 is joinedthrough two lateral wing portions to the main portion of the finger 3,which carries the laterally projecting articulating trunnions 32. Thesewing portions enable the spring 36 to be guided. The wedge-shaped end ofthe finger 3 has a rounded internal face (FIG. 9) for cooperation withthe ramp 30, and is offset axially with respect to the main portion ofthe finger 3.

The skirt 52 is slotted at 51 to provide a passage for the tape 8, thedepth of the slot 51, which in this example is a blind slot, being afunction of the height of the tape 8. This slot enables the tape 8 topass easily through.

One of the edges of the slot 51 is rounded at 50 so as to enable thetape 8 to be deflected thereon without damaging the tape, in a manner tobe described later herein. The rounded portion extends between the skirt52 and the hub 2

The outer rotor 6 is again of annular form, and accordingly it has anannular skirt 65 which is joined in its upper portion (FIG. 1) to atransverse flange 64 which carries two external, axially projectingprongs 61, 62 of unequal length, which together constitute a fork 63. Inthis example, the prong 62 has a lesser height than the prong 61, thesaid prongs 61, 62 being offset circumferentially with respect to eachother.

It will be noted that the hub 2 also has on its outer periphery aprojecting set of teeth 20, referred to as an outer set of teeth, in theregion of its flange 21., these teeth being a discontinuous set in thisexample. The set of teeth 20 is formed in a thickened portion 22 of thehub 2, at the outer periphery of the latter in the region of its flange21. The thickened portion 22 defines a transverse abutment shoulder forthe sleeve 56 of the inner rotor 5. The set of teeth 20 is notcontinuous over a circle, by contrast with the set of teeth 40, which isitself continuous, that is to say it is a complete set. The set of teeth20 can of course be continuous on a circle, depending on theapplication.

The skirt 65 is of course also provided with a passage means 60, whichin this example is a slot, for the flexible tape 8, with the outer rotor6 surrounding the inner rotor 5.

Thus, the epicyclic gear train consists in this example of the sets ofteeth 40, 20 and the pinion 4, which is mounted for rotation on thespigot 53, which is cylindrical and which thus constitutes a fixedtrunnion of the inner rotor 5.

If necessary, further pinions can of course be provided, these being forexample spaced apart at 120 degrees with respect to each other.

The pinion 4 is thus mounted for rotation on the trunnion 53, and drivesthe inner rotor 5 in stepping rotation in cooperation with the partialset of driving teeth 20 of the hub 2 and the fixed full set of teeth 40of the housing 7.

The conjugation of the three elements 40, 20, 4 constitutes an epicyclicgear train having a step-up gear ratio in the proportion of the sum ofthe diameters of the hub and the inner rotor mounted on the hub.

If d1 is the outer diameter of the hub and d2 the outer diameter of theinner rotor, then the reduction ratio is equal to (d1+d2)/d1.

As will have been understood, the number of teeth in the set of teeth 20on the hub (formed in the upper portion of the hub 2) is defined so asto obtain the step-up gear ratio which is matched to the dimensions ofthe rotary contactor, so that the set of teeth 20 may or may not becontinuous.

The projecting driving finger 3 of the inner rotor 5 is adapted so as tocooperate with the ramp 30 having the double slope mentioned above, orcam, which is situated within the housing 7 in the upper portion of thelatter, as is the set of teeth 40 which meshes with the complementaryset of teeth of the pinion 4.

The outer diameter of the flange 54 is of course such that it does notinterfere with the prongs 61, 62 of the fork 63, which is accordinglylocated radially between the flange 54 and the ramp 30. Also as aresult, the outer rotor 6 includes, as an axial extension of itsthickness with respect to its flange 64, an integral, internal centeringsleeve 66 at the inner periphery of the flange 64.

The sleeve 66 has an internal bore the diameter of which is smaller thanthat of the skirt 65. The sleeve 66 thus enables the outer rotor 6 to bemounted for rotation on the inner rotor 5 (i.e. on the skirt 52 of thelatter), while defining a space between the rotors 5, 6 foraccommodating the flexible tape 8. There is of course also a spacebetween the internal bore of the housing 7 and the outer rotor 6 toenable the tape 8 to be wound on to the rotor 6, which thus providesgood support for the tape 8.

In this example, the tape 8 is an extruded multiconductor cable, theflexibility of which provides the return function necessary for theprinciple of operation of the rotary contactor. Its two ends are bentback at 90 degrees in order to enable it to pass directly out to thecircuitry connections (the connectors), thus avoiding the need for anyintermediate connection (FIG. 10).

The zones bent back at 90 degrees are molded on to the above mentionedportions 80 and 81 of the housing 7 and hub 2, so as to guarantee therequired geometry and also to provide positioning and retention of thehub 2 in the chimney 70 and in the housing 7.

The electrical insulation of the tape 8 is preferably of a generallysilent material having a low coefficient of friction. It is based forexample on polyamide 11 or on a copolymer of ethylene andtetrafluorethylene which is stable at temperatures in the range between--55° and 150°. The electrical conductors of the tope are preferablyflat wires.

The ring 1 mentioned above enables final assembly of the rotarycontactor to be obtained by clipping it on to the chimney 70 of thehousing 7. The ring 1 thus ensures retention and enables the componentsof the contactor to rotate.

Thus, in this example, the flexible tape 8 is applied by molding to thehub 2 and the housing 7 respectively, and a disconnectable rotarycoupling is obtained between the rotors 5, 6 by virtue of the finger 3and the prongs 61, 62, in a manner to be described below.

Taking as the starting point for the rotational movement one of theextreme positions shown in FIGS. 3 and 6 and the left hand position inFIG. 9, the central hub 2 is driven in rotation by the steering wheel ofthe vehicle and pulls on the tape. The set of teeth 20 of the hub 2drives the pinion 4, carried by the inner rotor 5, in rotation. Thispinion engages on the similar, fixed set of teeth 40 located inside thehousing 7 in the upper part of the latter, thus driving the inner rotor5 in rotation. The outer rotor is stationary during this phase.

When the inner rotor has performed one revolution, the driving finger 3,fitted on the flange 54 of the said rotor 5 and driven by the latter,meets the fixed double-sloped ramp 30 (see FIG. 7 and the mean positionin FIG. 9), located on the smooth portion 71 of the said housing 7, sothat the finger can then, against the action of the spring 36, mountover the first prong 62 carried by the outer rotor 6, so that it thencomes into abutment (see FIG. 8) on the second prong 61, shorter thanthe first prong 62, so as to drive the outer rotor 6 in rotation. Theouter rotor, driven in this way, performs one revolution.

The distance between the prongs 61, 62 is of course a function of thethickness of the finger 3 (see the left hand part of FIG. 9), in orderthat the said finger 3 can be lodged between the two prongs 61, 62.

After the two revolutions of the inner rotor 5 and one revolution of theouter rotor 6 have been made, the hub 2 has rotated through a number ofturns equal to or greater than five.

The number of revolutions of the hub 2 is thus determined by its outerdiameter, and then by that of the two rotors 5, 6.

This dimensioning enables the step-up gear ratio of the epicyclic geartrain 40, 20, 4 that is to be adopted in order to obtain correctdimensioning of the apparatus, to be determined.

As will have been understood, the epicyclic gear train 40, 20, 4 is of adouble differential kind, due to the presence of the prongs 61, 62 andthe finger 3 held by the bridge element 31.

For the other extreme position (FIG. 4), and the left hand position inFIG. 9, the direction of rotation of the hub 2 is reversed. The whole ofthe tape 8 is wound on to the hub 2.

The drive finger carried by the inner rotor 5 is positioned by the twoprongs 61, 62 of the fork 63 of the outer rotor 6 (FIGS. 8 and 9). Thetwo rotors 5, 6 are thus coupled together in rotation.

The rotation of the hub 2 drives the epicyclic gear train 40, 20, 4 inrotation, and this itself causes the inner rotor 5 to rotate so as todrive the outer rotor 6 in rotation.

At the end of a first revolution (FIG. 5), the driving finger 3 israised by the pointed ramp 30 of the housing 7, thus disconnecting therotational coupling between the rotors 5, 6.

After this, the inner rotor 5 is driven in rotation through onerevolution by itself, so as to regain its original position (FIG. 3).Thus in the original position (FIGS. 3 and 10), the tape 8 is drawn asfar as the slot 51 and is then turned, by virtue of the rounded portion50, before being wound on to the skirt 52 in approximately one turn. Asecond turn is formed on the skirt 65 of the outer rotor 6, the tapehaving previously passed through the slot 60.

In FIG. 4, the tape 8 is wound on to the hub 2 and passes over therounded portion 50 so as to pass through the slots 51, 60 which are incorresponding relationship with each other. In FIG. 5, the tape is woundon to the hub 2 and on to the outer rotor, passing through the slots 51,60.

Thus, thanks to the invention, the device for multiplying turns, basedon the double differential principle, gives a gain in tape length in aratio that lies in the range between 6 and 10, the ratio 10corresponding to an arrangement in which the diameter of the hub 2 islarge, and the ratio 6 to an arrangement in which the diameter of thehub 2 is small.

It will be appreciated that all this is obtained without anymicrofractures, due to the advantageously low coefficient of friction ofthe insulation of the tape 8.

It will be appreciated that the arrangement is less noisy than that inthe prior art, because the tape is shorter and the hollow rotors aresimple components with a skirt on which the tape is wound, together withan axially oriented centering sleeve inside the skirt, for the rotarymounting of the rotor on the hub and on the inner rotor respectively,defining a space for the tape. The length of the sleeves 56, 66 dependson the application. In this example, the sleeves 56, 66 are short, andconsist of collar portions, while the end of the chimney 70, close tothe base 74 of the housing 7, is preferably of stepped form and hascylindrical centering portions on which the free ends of the skirt 52and the skirt 65 are respectively fitted.

Thus, the rotors 5 and 6 are mounted for rotation at each of their freeends on the stepped chimney 70, and at their other end, by virtue of thecollar portions 56, 66, on the hub 2 and on the inner rotor 5respectively.

The presence of the outer rotor does of course depend on theapplication, and a single rotor may be provided.

It will be appreciated that, despite the thickness of the inner rotor 5,the external diameter of the contactor can be reduced due to the factthat the tape is shortened, given that the latter is mounted withclearances within the housing 7 in the same way as a watch spring.

An improved reduction in overall size is obtained with the two rotorsbecause the presence of the second rotor, in spite of its thickness,enables the tape to be shortened and enables even more space to be

A double differential motion transmitting device between the housing 7and the hub 2 is obtained by virtue of the two rotors, the epicyclicgear train, and the disengageable rotational coupling between the saidrotors, so that the epicyclic gear train is of a double differentialtype.

It will be appreciated that the tape 8 is conserved., because it windson to the hub 2 and the skirts of the rotors 5, 6. It is thus wellsupported, with its winding action taking place in a circular mode. Thedepth of the housing 7 is small.

I claim:
 1. A rotary contactor, especially for motor vehicles,comprising:two coaxial parts which are mounted for rotation of one withrespect to the other against the action of an electrically connectingflexible tape which is wound in a spiral between the coaxial parts,being attached at one of its ends to one of the coaxial parts and at itsother end to the other one of the coaxial parts, wherein one of thecoaxial parts comprises a rotatable hub, and the other coaxial partcomprises a hollow fixed housing containing the hub within it, andwherein the fixed housing includes an axially oriented annular skirt,within which there is formed a set of internal teeth constituting partof an epicyclic gear train, which also comprises a set of teethprojecting from the outer periphery of the hub together with at leastone pinion for meshing with the set of internal teeth of the fixedhousing and with the set of teeth of the hub, the train enabling thenumber of revolutions between the movable hub and the fixed housing tobe demultipled, wherein the pinion is carried in rotation by an innerrotor of hollow annular form having an axially oriented annular skirt,the inner rotor being mounted in rotation on the movable hub within thefixed housing, wherein there is a space between the movable hub and theinternal bore of the skirt of the inner rotor for accommodating the tapeand for winding of the tape around the movable hub, and wherein theskirt of the inner rotor has a passage for the flexible tape, the tapebeing adapted to wind on to the skirt of the inner rotor; an outer rotorof hollow annular form disposed inside the fixed housing and surroundingthe inner rotor; and a rotary coupling acting disconnectably between theinner rotor and the outer rotor so that the epicyclic gear train is of adouble differential type.
 2. A rotary contactor according to claim 1,wherein the inner rotor carries a spigot for rotary mounting of thepinion thereon, the set of teeth of the housing is continuous, while theset of teeth of the hub is discontinuous.
 3. A rotary contactoraccording to claim 1, wherein the passage means comprises a slot formedin the skirt of the inner rotor, and one of the edges of the slot has arounded portion for redirecting the tape.
 4. A rotary contactoraccording to claim 1, wherein the inner rotor has at one of its ends atransverse base and a sleeve for the centering and rotary mounting ofthe inner rotor on the hub.
 5. A rotary contactor according to claim 1,wherein the outer rotor has an annular skirt which is slotted to allowthe flexible tape to pass through, the slot begin formed in an annularskirt of the outer rotor, for winding of the flexible tape thereon.
 6. Arotary contactor according to claim 1, wherein the inner rotor carries adriving finger which is adapted to cooperate with prongs carried by theouter rotor.
 7. A rotary contactor according to claim 6, wherein theprongs of the outer rotor are of different heights.
 8. A rotarycontactor according to claim 6, wherein the driving finger is adapted tocooperate with a ramp carried internally by the housing.
 9. A rotarycontactor according to claim 6 wherein the outer rotor is mounted forrotation on the inner rotor by a centering sleeve mounted on an annularskirt of the inner rotor, for winding of the flexible tape thereon. 10.A rotary contactor according to claim 6, wherein the driving finger ismounted for tilting movement on the inner rotor by a bridge element ofthe inner rotor.
 11. A rotary contactor according to claim 10, whereinthe driving finger has at one of its ends two lateral trunnions formounting in cradle elements fixed to the bridge element.
 12. A rotarycontactor according to claim 10, wherein the driving finger is acted onby a return spring, which bears on a bridge portion of the bridgeelement and on the upper portion of the driving finger.
 13. A rotarycontactor according to claim 12, wherein the driving finger iswedge-shaped at its other end, for cooperation with a pointed rampcarried internally by the housing.